1. Field of the Invention
The present invention generally relates to multi-piece golf balls and more particularly to golf balls having at least one layer made of polyamide/fatty acid salt compositions. The golf ball includes a core having at least one layer and cover having at least one layer. Preferably, the ball contains a dual-core having an inner core and surrounding outer core layer or a multi-layered core having an inner core, intermediate core layer, and outer core layer. Preferably, at least one of the core layers is formed from a composition comprising a blend of polyamide and fatty acid salt.
2. Brief Review of the Related Art
Multi-piece, solid golf balls are used today by recreational and professional golfers. Basically, these golf balls contain an inner core protected by a cover. The core acts as the primary engine for the ball and the cover helps provide the ball with durability and wear-resistance. The core and cover may be single or multi-layered. For example, three-piece golf balls having an inner core, inner cover layer, and outer cover layer are popular. In other instances, golfers will use a four-piece ball containing a dual-core (inner core and surrounding outer-core layer) and dual-cover (inner cover layer and surrounding outer cover layer). Intermediate (casing) layer(s) may be disposed between the core and cover layers to impart various properties. Thus, five-piece and even six-piece balls can be made. Normally, the core layers are made of a natural or synthetic rubber material or highly neutralized ionomer polymers (HNPs). These ionomer resins are typically copolymers of an olefin such as ethylene; and an unsaturated carboxylic acid such as methacrylic acid, acrylic acid, or maleic acid. Metal ions such as sodium, lithium, zinc, and magnesium are used to neutralize the acid groups in the copolymer. The acid groups may be partially or fully neutralized.
Such ethylene acid copolymer ionomer resins are relatively hard materials having good durability, cut-resistance, and toughness. The ionomers may be used to make cover, intermediate, and core layers. When used as a core material, the hard ionomer resin helps impart a higher initial velocity to the golf ball. This is particularly advantageous for driver shots off the tee. The ball tends to have good flight distance. However, one disadvantageous feature of such balls is they tend to have a hard “feel.” Some players experience a harsher, less comfortable feel when their club face makes contact with these hard balls. The player senses less control and the harder ball tends to have low initial spin. It is generally more difficult to hit hard balls with the proper touch and spin. This can be particularly troublesome when making approach shots with irons near the green.
Manufacturers of golf balls have looked at making blends of ethylene acid copolymer ionomer blends with softer, non-ionomer polymers to modify the properties of the ionomer resin so that it can provide a better feel to the golf ball. For example, Morken and Talkowski, Published PCT Application WO 2010/002684 discloses a composition comprising an ionomer and a polyamine or a tertiary polyamide, which may be used in golf ball constructions. The tertiary polyamide has a molecular weight of greater than 500 Da and does not contain any secondary or primary amide moieties. The ionomers are preferably ethylene acid copolymers or E/X/Y copolymers where E represents copolymerized units of ethylene, X represents copolymerized units of the α,β-ethylenically unsaturated carboxylic acid, and Y represents copolymerized units of a softening comonomer. The composition may further include organic acids or salts of organic acids. Suitable organic fatty acids are described as including palmitic, stearic, oleic, erucic, behenic acids, and mixtures thereof. The composition may be used in core, mantle, and/or cover layers for golf balls.
Kim et al, U.S. Pat. No. 7,528,196 discloses golf balls having a core, one or more intermediate layers, and an outer cover layer, wherein at least one of the layers is formed from a composition comprising at least one polyalkenamer rubber and at least one polyamide. Nylon 6, nylon 11, nylon 12, nylon 4,6; nylon 6,6; nylon 6,9; nylon 6,10; and nylon 12 are described as being suitable polyamides. Preferably, polyamide elastomers (copolymers of a polyamide and polyester or polyether) are used. The layer may further comprise one or more ionomer resins. The ionomer resin may be prepared by mixing an ethylene acid copolymer which is neutralized with metal ions and from about 5 to about 40 weight percent of one or more fatty acid or metal salts of such fatty acids.
Rajagopalan et al., U.S. Pat. No. 6,774,184 discloses a golf ball comprising a core, intermediate layer(s), and a cover, wherein at least one of the layers is made from a polyamide composition comprising a blend of: i) a polyamide in the form of a homopolymer, copolymer or block copolymer, with the proviso that the polyamide polymer is not a block polyamide copolymer comprising main-chain polyether blocks, and ii) an ionomer resin. Preferably, the ionomer is a copolymer of an olefin and an α,β-ethylenically unsaturated carboxylic acid, wherein at least a portion of the carboxylic acid groups are neutralized with a metal ions.
Rajagopalan et al., U.S. Pat. No. 6,756,436 discloses a golf ball comprising a core made of a an ionomer acid copolymer neutralized by a fatty acid or fatty acid salt (preferably a salt of stearic, behenic, erucic, oleic, or linoleic acid, or dimerized derivatives thereof) being present in an amount sufficient to neutralize the copolymer by at least about 80%. The core has a compression of no greater than about 80, and a diameter of no less than about 1.53. The ionomer acid copolymer may be blended with a second polymer component including polyamides.
Chen, U.S. Pat. No. 6,562,906 discloses compositions of partially or fully neutralized blends ethylene α,β-ethylenically unsaturated C3-8 carboxylic acid high copolymers having molecular weights of about 80,000 to about 500,000; and ethylene α,β-ethylenically unsaturated C3-8 carboxylic acid low copolymers (Mw of about 2,000 to about 30,000). Optionally, the composition may contain thermoplastic elastomers including copolyetheramides; and organic acid salts including fatty acid salts such as salts of stearic, behenic, erucic, oleic, and linoleic fatty acids.
Although some polyamide/ionomer compositions may be somewhat effective for making core layers and other components in a golf ball, there is still a need for new compositions that can impart high quality performance properties to the ball. Particularly, there is a continuing need for improved core constructions in golf balls. The core material should have good toughness and provide the ball with high resiliency. The core material, however, should not be excessively hard and stiff so that properties such as feel, softness, and spin control are sacrificed. The present invention provides golf balls having an optimum combination of properties.